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Guidance to Effective Acoustic Leak Detection
All acoustic leak detection methods are based on the premise that normal water passage through pipelines
takes place noiselessly. When the water passage is disturbed a noise is created. Causes can include partial
pipe blockages, sudden changes in pipe diameter, abrupt changes in pipe direction, pumps or meters installed
in the pipeline, consumer usage or pipeline damage. Pipeline damage can include holes, cracks or splits,
complete pipeline rupture, leaking joints or leaking valves.
Careful application of leak detection techniques will enable the operator to eliminate detected noises
generated by poor pipeline design or consumer usage and to identify leakage due to pipe system damage.
The strength and clarity of noise generated by leaks will be affected by the water pressure, the size and shape
of the orifice allowing leakage, the type of ground material around the pipeline, the type of ground cover over
the pipe, the diameter, wall thickness and material of the pipeline and the quantity of water leaking.
A small orifice or hole and high water pressure generally produces a higher frequency noise. Often the noise
level increases around valves, pipe elbows, T-connections and pipe ends, etc… since the partial obstruction
increases pressure and creates some further disturbance in the water path.
Leak noise is transmitted along the pipeline both through the water and the pipe wall as well as into the
ground around the pipe. The noise travels much better through "hard" materials: further along metallic pipes
than asbestos cement pipes which themselves are better than plastic pipes. Ground material generally
provides a poorer travel path than the pipeline itself. Soft sandy ground provides a worse travel path than well
compacted ground with a hard-paved surface covering.
The leak noise can change in strength and pitch as it travels along the pipe or through the ground. The deeper
the pipe is buried and the softer the ground the more the noise will be dampened.
When a leak is produced in a metallic pipe the leak noise will transmit well through the pipe. It does not travel
so well through a plastic pipe. This means that a leak noise can be heard further away on metal than on
plastic. Also bear in mind that the further you go from a leak noise source the more difficult it is to pinpoint that
leak noise accurately.
Background noise can interfere with leak detection. Traffic and machinery noises can travel for considerable
distances through both air and ground material and often occur in the same frequency bands as leak noise.
Sometimes it is necessary to use leak detection techniques at night when interfering noises are less.
It is very important to adopt a methodical approach when using any instrument for acoustic leak detection. It is
necessary to practice the technique in order to distinguish between different sounds, recognising background
or interfering noises, so that they can be eliminated. It is also essential that other (non-leakage) system noise
sources such as consumer draw-off or partially closed valves be eliminated by logical site inspection practices
prior to any excavation taking place.
LEIF KOCH A/S • Rugvænget 31 • DK-2630 Taastrup • Telefon: (+45) 7023 9898
info@leifkoch.dk • www.leifkoch.dk • CVR: DK 78 06 64 15